Many variants of control modules with digital outputs are already known. A digital output can thereby have one of the two digital states “digital ONE” or “digital ZERO”. The control module controls the load connected to the digital output depending on the state of said digital output.
In automation systems such control modules are used for example to activate a very wide range of actuators, e.g. electromagnetic components and in particular also signal generators. Such actuators have a specific load resistance and are in some instances connected together with a current-limiting series resistor via the corresponding electrical connection to one of the digital outputs of the control module.
If such signal generators are used in automation systems for monitoring purposes for example, the digital output will have one of the two digital states depending on operating state. For example in the case of a fire alarm in normal operation of the automation system, the output of the control module will have the “digital ZERO” state, while in the event of a failure, the “digital ONE” state is present at the output and the signal generator is therefore activated.
If an interruption now occurs between the electrical connection and the signal generator due to a wire break, the actuator can no longer be controlled by the control module and a malfunction results with the failure of the automation system. If, as in the case of the signal generator in the form of a fire alarm, the “digital ZERO” state corresponds to the normal operating state and the “digital ONE” state occurs only rarely, such a malfunction is not identified for quite a long time without additional monitoring. In order to establish such a malfunction promptly, it would be conceivable to send an additional test signal to the electrical connection at regular intervals to test whether the load is still securely connected to the electrical connection.